What is the sealing film?

In the world of flexible plastic packaging, the sealing film is the "invisible guardian" that silently protects the top of the container. It's like a custom-made coat that tightly wraps around the tops of jelly cups, yogurt cartons, medicine bottles, and fast food boxes, using its own body to shield the contents from external intrusions.

The "body" of the sealing film is composed of multiple layers of composite materials (such as PET, NY, CPP, aluminum foil, etc.). Each layer has a unique mission: some are responsible for moisture resistance, some for anti-oxidation, and others can maintain toughness under extreme temperatures. It closely bonds with the container through heat sealing or ultrasonic sealing technology, ensuring both airtightness and allowing users to easily tear it open.

Why is the sealing film important?

Although the sealing film is just a thin sheet, it is the "unsung hero" behind the product's shelf life, usability, and safety:

Sealability: It is the "raincoat" for the contents, preventing moisture absorption, oxidation, or contamination and extending the shelf life;

Ease of Tearing: It "cares about users" and allows yogurt lids to be easily peeled off with a peeling force of 4-6N, leaving no annoying residues;

Temperature Resistance: Whether it is a high-temperature cooking environment of 121°C or a freezing environment of -18°C, it can remain stable;

Barrier Property: It is like an "invisible barrier" that uses high-barrier materials (such as EVOH, PVDC) to isolate oxygen and water vapor and protect sensitive contents.

How does the sealing film work?

The "body structure" of the sealing film is the secret to its functionality:

Outer Layer: High-strength materials (such as PET, BOPP) are its "face", providing both a printing surface and mechanical support;

Middle Layer: The barrier layer (aluminum foil, aluminized film, NY) is its "protective shield", enhancing the anti-permeability;

Inner Layer: Heat-sealing materials (PE, CPP, EVA) are its "adhesive", ensuring a tight seal with the container.

Its "growth process" is equally crucial: it needs to go through 10 hours of natural curing and 72 hours of high-temperature curing to make the materials of each layer "join hands" and form a strong bonding force.

Classification Criteria and Types (The "Family Members" of the sealing film)

The family members of the sealing film can be divided into several categories according to their functions and material properties:

Classification by Function:

Easy-to-tear sealing film: It is a "thoughtful assistant" that uses modified resins (such as EVA, EMA) to achieve "easy peeling without residues", suitable for ready-to-eat products like yogurt and jelly;

Non-easy-to-tear sealing film: It is a "long-term guardian", mostly used for pharmaceuticals or industrial products, but it is gradually being phased out due to its inconvenience of use.
Anti- fog sealing film: Cold anti-fog film: Suitable for low-temperature environments (such as refrigeration), it prevents water vapor condensation through a hydrophilic coating or hygroscopic structure. For example, PE anti-fog film maintains transparency at low temperatures by forming a uniform water film.

Hot anti-fog film: Used in high-temperature scenarios (such as cooking packaging), it enables water droplets to slide off quickly through hydrophobic treatment or the addition of anti-fog agents, preventing fogging. For instance, PP material is more suitable for such scenarios due to its high-temperature resistance.

Functional sealing film: Compatible with All Materials of PP/PE/PET tray

Classification by Material Composition

Single-material sealing film: It is an "economical player", such as PE/PE, CPP/PP. It has a low cost but single functionality, suitable for ordinary moisture resistance needs;

Composite-material sealing film:

High-barrier Type: Such as PET/AL/PE (used for bowl porridge, high-speed rail lunch boxes), with an oxygen barrier rate of <0.5 cm³/(m²·24h·0.1MPa);

High-temperature-resistant Type: Such as PET/NY/SRCPP (used for foods cooked at 121°C), which needs to pass the backpressure test to prevent deformation.

Classification by Operating Temperature

Ordinary Grade (<80°C): Suitable for sealing films of refrigerated yogurt;

Boiling Water Grade (80-100°C): Can withstand pasteurization and is commonly found in jelly packaging;

High-temperature Cooking Grade (121-135°C): Such as the PET/AL/CPP structure, used for canned goods and instant rice.

Classification by Application Field

Food Category: Complies with FDA standards, such as PET/NY/PE used for jelly and HDPE paper-like film used for fast food boxes;

Pharmaceutical Category: Emphasizes sterility, such as PET/AI/PE used for sealing medicine bottles;

Industrial Category: Such as PVC sealing films resistant to chemical corrosion used for chemical products.

"Working Scenarios" of the sealing film

The sealing film can be found in various industries:

Food Industry: Jelly (PET/NY/PE), bowl porridge (PET/AL/SRCPP), frozen foods (NY/PE);

Pharmaceutical Industry: sealing films for medicine bottles (PET/AI/PE), packaging for sterile syringes;

Daily Necessities: Sealing for barreled water (PET/paper/AL/PE), sealing films for cosmetic bottles.

The "Circle of Friends" and Future Trends of the sealing film

The "circle of friends" of the sealing film includes material suppliers (such as DuPont's APPEEL modified resin, Toyo's TOPCO heat-sealing adhesive) and environmental innovators (such as degradable sealing films with PLA substrates). Its future is full of hope:

Environmental Innovation: Degradable sealing films and smart packaging (integrated with temperature and humidity sensors) are on the rise;

Process Upgrade: Coextrusion technology (such as BOPE film) makes the sealing film more transparent and more puncture-resistant, suitable for fresh produce packaging.

The sealing film is an indispensable "guardian angel" in the flexible plastic packaging family. Its design needs to find a balance among functionality, cost, and environmental protection. In the future, with the popularization of single-material solutions (such as BOPE) and smart packaging technologies, the sealing film will continue to evolve towards high performance and sustainability, and will continue to safeguard human life.

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